Merck (MRK 0.09%) has been in the spotlight recently with the announcement of positive results for its COVID-19 pill developed with Ridgeback Biotherapeutics. Pfizer (PFE -0.43%) is also evaluating an oral COVID-19 therapy and could be hot on the heels of Merck. In this Motley Fool Live video recorded on Sept. 29, 2021, Motley Fool contributors Keith Speights and Brian Orelli discuss four key things investors should know about Pfizer's experimental COVID-19 pill.

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Keith Speights: Pfizer had more news on Monday. The company announced that it's started a phase three study evaluating PF-07321332. Don't make me say that again. But Pfizer has started this study evaluating the therapy co-administered, by the way, with a low dose of ritonavir which is an antiviral therapy. This is for the prevention of COVID-19 infection.

We've talked about this before, Brian, but what are the key things investors should know about this experimental COVID-19 pill and it's commercial prospects.

Brian Orelli: The primary four things to think about. One, this is the clinical trials, is testing it as a prophylaxis. These are people who might have been exposed but they don't have any symptoms. Then they're testing it for five days or ten days and comparing that to placebo and seeing whether the people end up developing COVID-19.

Two, that additional drug that you mentioned, ritonavir is used in combination with other drugs including in HIV regimens. It doesn't actually work on the virus. It works on a human protein that breaks down protease inhibitors. There's PF-'332 is a protease inhibitor. That drug is making the active drug, the PF-'332, stick around longer. That's the reason why they're giving a low dose of that.

Three, Pfizer is also testing this drug in patients who have COVID-19. Those studies are ongoing and I think that's probably a bigger market for the drug than as a prophylaxis. But there will be some people who are exposed and then want to take the drug, but we'll have to wait and see how much it's actually helping those patients. I guess, they're not even patients at this point.

But I think that whether it can get people out of the hospital faster or in patients who aren't in the hospital, keep them from going into the hospital, that's a much higher value play. I think Pfizer can charge more if it can help those patients versus a prophylaxis.

Finally, Pfizer has competition in the oral market. Merck and Ridgeback have an oral drug. Although their drug, I don't think it is designed specifically to attack the coronavirus. We'll have to wait and see whether Pfizer or Ridgeback was the one that designed the drug and which one of those two drugs works better.

Roche (RHHBY 0.43%) and Atea (AVIR -2.43%) have a drug that works through a completely different mechanism. Maybe there's a potential that Roche and Atea's drug could get combined with Merck's drug or with Pfizer's drug. We'll have to wait and see in there. I don't think they are testing them as a combination yet. They probably wouldn't need to prove that each one of them works individually and then they could do those tests.

Speights: Thanks, Brian. Those are four great things for investors to know about Pfizer's COVID-19 pill program. The company is moving pretty quickly on this. Pfizer has said that if all goes well, it could actually file for emergency use authorization by the end of this year. We should know some news relatively soon about how this pill is working.

Orelli: Yeah. That would be for treatments not for prophylaxis; the clinical trial that they just started that will take a little longer.